The detection of a malfunction in a digital system comprising a digital circuit connected to and communicating via a bus, may be evident by an incorrect or absent response to an interrogation request via the data bus. The malfunction may due to the failure of the digital device or failure of the power supply feeding the device. Detection of the failure may result in some form of protective action, to prevent the propagation of the erroneous state via the communication bus, and to cause the device and or system of which it is a part, to change from the current state to a protective condition.
A television receiver, or VCR, often contain multiple protection circuits which monitor various parameters and often provide protection by shutting down or turning off the power supply in the apparatus, or by placing the apparatus in a standby non-operational mode. Most protection systems employed in prior television receivers use electronic components to sense malfunctions and control the protective means. These components add complexity to the circuit design, introduce a potential for greater unreliability, and increase the material cost of the product. The object of this invention is the provision of a detection and protection method whereby failures of a power supply or digital circuit are detected without additional parts specific to failure detection.
It is known that television receivers may employ separate power supplies often termed a standby supply and a run or operational supply. The standby supply is active continuously whenever the apparatus is connected to an external AC mains supply. The standby supply powers systems which must remain active when the apparatus is turned off. Such systems are termed standby loads and may include the remote control receiver, the on/off switching means, digital clocks, volatile memory, and a digital processing means such as a microcomputer.
The run supply powers the operational or run loads which are only active when the apparatus is on. These run loads may include the tuner, IF amplification, synchronization and electron beam and scanning generation, video and audio processing etc.
In many instances, the television receiver will include standby and run power supplies. The standby power supply is connected to an AC mains supply, however, the run supplies are generated by rectification of horizontal frequency pulses coupled via a transformer in the collector of the horizontal output transistor. Any undue loading of the run supply, due to short circuit or component failure in one of the operational loads will be coupled, via the horizontal output transformer, to the other operational supplies. Thus, undue loading or failures in any run supply or operational load, will result in a reduction in the power supplies coupled to the other loads including digital circuitry of the tuner unit.
A microprocessor may be coupled to the standby power supply and control switching between a run mode wherein the standby and run power supplies are operative, and a standby mode wherein only the standby supply is operative. Mode switching may be originated manually by the user, via input switch selection or by remote control command, or automatically by the microprocessor sensing a fault condition. The microprocessor is in digital communication with a digital circuit such as a phase locking tuner, via a bidirectinal data bus.